1. Field of the Invention
This invention relates generally to RF antennas operating a microwave frequencies and more particularly to a horizontally endfire array of crossed slot radiating elements.
2. Description of Related Art
Endfire antenna arrays for radiating electromagnetic energy coplanar with a ground plane at microwave frequencies are generally known. One such antenna is shown and described, for example, in U.S. Pat. No. 6,501,426, entitled xe2x80x9cWide Scan Angle Circularly Polarized Arrayxe2x80x9d, issued to Timothy G. Waterman, the present inventor, on Dec. 31, 2002. Disclosed therein is an array of dual trough radiator elements including orthogonally crossed trough waveguide cavities and RF feed members of predetermined adjustable length extending across the cavities from one radiator element to its neighbor. Feed members are suspended in a slot formed in the body of the radiator elements and the inner or proximal ends are connectable to an RF source via a feed point, while the outer or distal end is open circuited. The array also includes intermediate support members of electrical insulation located on the outer surface of the radiator element and a parasitic ground plane consisting of a set of parasitic conductor elements is located on the top surface of the intermediate support members so as to enable scanning of the array to or near endfire when energized.
In one aspect, the present invention is directed to a horizontally polarized endfire antenna array providing 360xc2x0 scanning over a ground plane and comprised of a plurality of radiating cavity backed slots formed by a plurality of mutually separated flat, typically rectangular or triangular, segments of metallization arranged in a grid and supported by a layer of dielectric material in a coplanar arrangement above the ground plane. The metallic segments are shorted to the ground plane at their centers. The side edges of the metallic segments define a plurality of substantially linear crossed slots running in at least two, e.g. orthogonal, directions. Each element of the array consists of a plurality, four or more, of adjacent metallized segments having mutually opposing inner corners surrounding a common feed point. RF launch points for the array are formed across the slots of pairs of neighboring segments by elongated electrically insulated launch point conductor elements connected to respective common feed points and running beneath the segments and extending open circuited across a respective slot at their midpoints.
In a further aspect of the invention, two floating parasitic conducting elements are located in and around the area where the slots cross so as to make the array operate more effectively and comprise a crossed segment of metallization fabricated on the surface of the dielectric layer and a loop of metallization embedded in the center of the dielectric layer beneath the crossed segment.
Yet another aspect of the invention is directed to a method of providing a horizontally polarized endfire radiation pattern, comprising the steps of arranging an array of radiator elements in a grid, wherein each of said radiator elements is comprised of a plurality of flat segments of metallization having side edges defining a predetermined number of crossed cavity backed slots and mutually opposing inner corners; locating the segments above a ground plane; shorting each of said flat segments to the ground plane; generating a plurality of launch points for contributing field vectors at each segment of metallization of said radiator elements from a respective common RF feed point located at at least two crossed slots of said predetermined number of crossed cavity backed slots and surrounded by said mutually opposing inner corners of said plurality of segments of the respective radiator element, by extending respective feed members extending across the slots from one segment of said plurality of segments of metallization to an immediate adjacent segment of each of said radiator elements for generating said launch points and connecting a same one end of said feed members of each of said radiator elements to said common RF feed point and leaving the other end open circuited.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific examples, while illustrating the preferred embodiments of the invention, they are given by way of illustration only, since various changes and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art from the detailed description.